low power comparator in nrf51.

[nordicbeginner]

hello there i want to use low power comparator nrf51. now my device work with battery. so i think i require internal reference. now can you tell me how to use internal reference??

[ovrebekk]

Hi

There is no internal reference option for the LPCOMP. You either have to use VDD * N/8 as reference (where N = {1,2,3,4,5,6,7}), or an external reference supplied through the AREF0 or AREF1 pin.

Are you trying to detect a low battery? If so you might want to use the Power On Fail feature instead.

Best regards
Torbjørn

[AmbystomaLabs]

In our experience the POF works well for triggering warnings for low battery and is internally tied to Vdd so you can implement in code. But with lithium button cells, the voltage varies quite a bit due to temp and processor activity. This can give early false detection when using POF. A little better solution is to use the ADC and measure Vdd and nRF core temp hourly or daily and use these data to drive a low battery solution. Similar to POF, the ADC can be tied internally to Vdd via the register settings so you can just implement in code.

[nordicbeginner]

yes i am trying to detect a low battery. can you tell me how to use power on the failure

[ovrebekk]

Using the ADC is definitely an option. Then you will also be able to use the internal 1.2V reference, for absolute measurements.